Removing change of a folder in Git

gistfile1.txt

Upgraded a dependency in a Git repository to an incompatible version but due to insufficient testing didn't notice until several commits later. I *could* have just done a simple revert but was bored and figured out how to wipe it from history completely (usual disclaimer, rewriting history in a repository you have shared with anybody else is not a nice idea).

To fix it:

* Put a copy of the original folder (i.e., the one you actually want) in a separate location. 
* Run the command in the script file below. This runs through each commit (so it could be very slow for a large repo), and checks if the new folder is present. If so, it deletes it and copies in the original. The tree-filter takes care of the Git add & rm commands as needed. The --prune-empty argument tells it to get rid of any empty commits (i.e., the one you committed the change in).

undo.sh

git filter-branch --prune-empty --tree-filter '
if [ -d newfolder ];
then
    rm -rf newfolder; cp -r /tmp/oldfolder .
fi'